I. Field of the Invention
The invention relates to the field of gas delivery systems and in particular to a method and apparatus for generating a pneumatic feedback signal to actuate a response upon the occurrence of an event.
II. Description of the Prior Art
Pressurized nitrogen is utilized in a large number of presently practiced industrial service and operational methodologies. In the field of aeronautics, for example, some of these applications include not only charging the aircraft tires and struts, but also charging or servicing a number of pneumatic control systems used throughout an aircraft. In the case of military aircraft, the number of such pneumatic control systems is substantially multiplied since the mission or functions which such aircraft serve are more complex and varied than those encountered in civil aircraft. Thus, in the case of military aircraft not only must the aircraft systems themselves be serviced or recharged with nitrogen, but often the aircraft carries one or more sophisticated weapons systems, which systems in turn also include a number of pneumatic actuators and controls which require charging.
Many of these systems require the injection of highly purified nitrogen or other gas in order to operate or reliably function in a wide extreme of environmental conditions. Therefore, various prior art devices have been developed wherein the gas is passed through a number of filters to remove particulate matter, and to reduce the level of contaminants, such as hydrocarbons and water, to an acceptable level. However, since the aircraft are serviced in the field, often under adverse environmental conditions, some means must be included to test the operation of the filtration system and to shut the system down or take other appropriate action in the event that contaminants begin to leak through the system. In any case, most filtration systems are cumulative and will eventually be saturated with contaminants. It is thus very important not to continue use of the system when the filters have become saturated, otherwise certain control systems or weapon systems within the aircraft might become charged with contaminated gas and fail to function.
Therefore, in order to build in such safeguards, the art has devised various systems wherein the contaminant flowing through the filtration system is sensed, and in the event that it exceeds a predetermined limit, the system is shut down. Such prior art systems, in the case of nitrogen delivery apparatus, have included electrical systems utilizing a nitrogen sensor which will, through appropriate control circuitry, actuate a solenoid powered electromechanical valve. Since the nitrogen charging system is usually mobile to deliver the nitrogen to the aircraft, such prior art systems are necessarily battery powered.
While such electrical control systems operate effectively, they are often complex, subject to failure when subjected to prolonged environmental exposure, and furthermore require that the battery pack be maintained in a charged condition. If in any event the battery should lose sufficient charge, the electrical control feedback system may malfunction with the result that contaminated nitrogen would be injected into the aircraft system without the operator's knowledge, or that at least the nitrogen servicing unit would be rendered inoperative until the battery could be recharged or replaced. This then results in a longer turn around or downtime for the aircraft which could otherwise be airborne.
What is needed then is a reliable and rugged method and apparatus whereby gas delivery apparatus may be monitored and controlled for contaminants without the shortcomings of the prior art as discussed above.